System and process for producing animal feed from food waste

ABSTRACT

A process is provided for producing animal feed from food waste by providing a dry, pelletized, fibrous organic material. Specifically, the invention relates to methods of thickening/dewatering solids that contain substantial amounts of moisture, e.g., ground food waste.

REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/981,261 filed Oct. 16, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to methods of producing animal feedfrom food waste by providing a dry, pelletized, fibrous organicmaterial. Specifically, the invention relates to methods ofthickening/dewatering solids that contain substantial amounts ofmoisture, e.g. ground food waste. More particularly, the inventionrelates to methods for thickening ground food waste as a water basedslurry utilizing synthetic organic flocculants usable as animal feedadditives. The invention also relates to methods of treatment of theseparated liquid phase (supernatant or filtrate) resulting fromthickening water based slurries.

BACKGROUND OF THE INVENTION

[0003] It is known in the art that an extrusion process that is a partof the food waste pelletization and drying technology cannot be providedwhen the liquid-solids admixture contains substantial amounts of liquid,e.g. water. U.S. Pat. No. 5,596,815 (Rice et al.) describes a method formoisture reduction by adding a dry material. This dry material adds tothe cost of the process.

[0004] U.S. Pat. No. 5,908,634 presents an animal feed in powder orgranular form containing molasses and 10 to 60% of bentonite andzeolite, which is added as a dehydrating agent, and causes the delayedrelease of nitrogen. Hydrated lime may be added as a source of calcium,to improve pellet quality. The addition of bentonite and zeolite asdehydrating agents require curing times of up to 12 hours, which is adrawback of the invention. Also, addition of the dehydrating agent inamounts of up to 60% diminishes the nutrient value of the animal feed.

[0005] U.S. Pat. No. 5,955,023 describes a method of forming a compositeparticle product from lignin-cellulose material bonded together withwater insoluble lignin (2-40% by weight) and a binding agent. Themixture is then heated and compressed to promote binding andcross-linking between the lignin binder and the lignin-cellulosematerial. Lignin functions as the primary adhesive for the product, andforming the particleboard product from the lignin bonding mixture. Thedrawback of the method is a necessity to use heat (between 100 and 240°C. for 1 to 60 seconds) to bind lignin with the cellulose material.Also, the initial lignin-cellulose material has to have a moisturecontent of about 30% or less, and water-insoluble lignin has to bedissolved in an organic solvent and then be evaporated.

[0006] U.S. Pat. No. 5,958,233 reveals a process and apparatus fordewatering aqueous solids residual after fermentation and distillation,such as corn stillage. The feed stream of aqueous solids slurry isfractionated into two or more sub-streams in such a way that one of thesub-streams contains predominately heavy particulate solids and hassubstantially improved free-draining characteristics. A secondsub-stream contains lighter particles, entrained fines of the heavyparticles, and a major portion of the liquid from the feed stream. Thefree-draining sub-stream is dewatered using a device such as a screencentrifuge or a screw press, both of which produce a cake of relativelyhigh solids content. The remaining liquid from the feed stream isconcentrated in an evaporator, before being mixed with the dewateredsolids, which may be dried to produce an animal feed. The drawback ofthe process is the loss of nutrients in the second sub-stream containinglighter particles to be potential animal feed unless the secondsub-stream containing lighter particles along with the liquid phaseseparated from the free-draining sub-stream are evaporated; evaporationof the liquid phases is not economical. Another drawback of the processis that it is limited to a fat free material, such as corn stillage, andthe method of dewatering of the free-draining sub-stream cannot be usedfor a material rich in fat unless the free-draining characteristics aresubstantially improved.

[0007] U.S. Pat. No. 5,976,594 discusses a process for turning foodwaste into animal feed including agitating the ground food waste in ablending tank so that the food waste is suspended. A production systemincludes a series of pipes and tanks through which food waste isprocessed and dehydrated so that the food waste is ultimately convertedinto animal feed. Dry feed stock is added as dehydrated material, andthe mixture is then converted into moist pellets that are then dried andpackaged for further distribution. The shortcoming of the process isinadequate dewatering of the food waste, resulting in large amounts ofdehydrating agent added, which makes the animal feed not economical.

[0008] U.S. Pat. Nos. 6,030,565 and 6,194,065 describe an agglomerateand a process for its manufacture by providing a dry, particulated,fibrous organic material that is mixed with a powdered mineral, thusresulting in the first mixture. A binding agent is added to the firstmixture, in order to obtain a second mixture. The agglomeration of thesecond mixture in an agglomeration dish and drying the agglomerateresults in a desired dried state. The drawbacks of the process are thatprocessing the fibrous organic material in a heated screw press, as wellas the addition of a binding agent, add to the cost of the finalproduct. Also, the agglomeration process requires the addition of abinding agent from the group consisting of chemical adhesives, resinsand starches, and these materials are not considered animal feed.

[0009] U.S. Pat. No. 6,106,673 provides a process and system for theseparation of a fermentation process by-product into its constituentcomponents. The process requires heating of a mixture containing theby-product to separate the oil from a base component of the by-product.Oil separation is followed by recovering the base product, the oil, and,possibly, other substances such as molasses from the mixture byevaporation (at a temperature between 140° F. to 250° F.). The drawbackof that process is excess energy consumption.

[0010] U.S. Pat. No. 6,132,625 provides a method that can be used toclarify substantially aqueous streams and optionally separate biosolids,especially proteins, from food processing operations. The methodcomprises the contact of an aqueous stream comprising biosolids with ananionic, inorganic, colloidal material selected from the group ofpolysilicate microgels, and an organic polymer (two cationic flocculantswith a low and high molecular weight), to flocculate the biosolids. Aprocess is provided which can be used to clarify substantially aqueousstreams and optionally separate biosolids, especially proteins, fromfood processing operations, which comprises contacting an aqueous streamcomprising biosolids with an anionic inorganic colloid and an organicpolymer, to flocculate the biosolids. A drawback of the invention isthat it is limited to a substantially aqueous stream containingbiosolids, especially protein. A quality animal feed will also containfats in an optimum ratio to proteins. If such an aqueous stream isseparated from the food waste, it may contain highly concentrated andhardly treatable organic material that could not be treated using onlythe synthetic organic flocculants.

[0011] U.S. Pat. No. 5,891,254 describes a method for purifying anaqueous sugar solution by a hydrolyzed polyacrylamide. The inventiondescribes clarification of sugar juice, related to the treatment of thesupernatant in the process modification described above. This referenceconsiders sludge to be a disposable residue, while the clear juice isthe ultimate product. The polymer binding solids is removed with wastesludge, and its effect on the final product (sugar juice) is negligible.The major drawback of the invention is that it is limited to sugar juiceproduction, and the sludge, when considered an animal feed, is processedto provide a necessary fat-to-protein ratio that is not a subject of thepatent. Another drawback of the invention is that it is limited to arelatively clear liquid, such as sugar juice containing primarilycarbohydrates. Such a liquid is treated with a hydrolyzed polymer, andthe method cannot be used for treating fat and protein contaminatedliquid unless an organic material destruction process is implemented.

[0012] U.S. Pat. No. 5,759,568 describes a method for producing animalfoodstuff from waste, and is based on addition of bentonite and apolymer to the waste stream. The reference describes the flow subject totreatment as a combination of, at least, three aqueous streams, so thatthe final stream can be very diluted. This is confirmed by the use of aflotation method for solids-water separation, resulting in the dischargeof the effluent to the sewer system. A substantial drawback of theinvention is that the flotation process results in separated solidscontaining abundant moisture, and the effluent containing residualsuspended solids. The reference does not disclose destruction of highlyconcentrated organic material resulting from separation of the solidcontaining both the fats and the proteins, so it is limited to thediluted streams. The reference assumes the use of filter presses (beltpresses) for sludge dewatering that significantly adds to the cost ofthe process. Nonetheless, the filtrate will contain abundant dissolvedresidual and colloidal organic material that has to be separated andtreated using a combination of the destruction and separation methods.

[0013] U.S. Pat. No. 6,132,625 assumes the use of a combination ofinorganic and organic coagulation-flocculation means for phaseseparation. The use of inorganic coagulants makes the ultimate productunusable as an animal food additive, resulting in the invention beingnot applicable for the purpose of making animal feed from the foodwastes.

[0014] U.S. Pat. No. 4,728,517 assumes production of animal feed fromfloat sludge and from activated sludge. Bulking agents, e.g. wood chipsand the like, added to remove fats as well as coagulation andflocculation agents are considered components of ultimate animal food.In this reference, the liquid phase (supernatant) is not removed fromthe system and is added to the batch. Thus, that liquid is evaporated,thereby inefficiently consuming substantial amounts of energy.

SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to provide a continuousprocess comprising shredding food waste containing fats without fatemulsification, followed by thickening of shredded (ground) food wasteusing an appropriate synthetic organic flocculant approved as an animalfeed additive. The thickened food waste is preferably a low moistureproduct subject to extruding (pelletization) followed by pellet excessliquid evaporation. The liquid phase separated in the thickening processis then treated, thus providing a high purity final effluent usable forrecycling, and excess sludge usable as animal feed additive.

[0016] A further object of the present invention is to provide acontinuous process of mixing the ground food waste with an appropriatesynthetic organic flocculent, followed by thickening.

[0017] A further object of the present invention is to provide a processfor treatment of the liquid phase resulting from the thickening processby a combination of the appropriate phase separation processes anddestruction and/or adsorption of the organic material.

[0018] In accordance with the above-noted objectives, the presentinvention is a system and process for producing animal feed from foodwaste comprising shredding (grinding) of the food waste, followed bythickening of ground food waste using an appropriate synthetic organicflocculent approved for animal food additives, thus resulting in a lowmoisture product, and treating the liquid phase by a method andapparatus providing high purity final effluent and excess sludge usableas animal food additive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a diagram of the sequential steps of the basic processof this invention.

[0020]FIG. 2 is a diagram of alternative raw waste collection andtransfer scenarios in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] A basic process of the invention is described as it relates tothe processing of food waste. As shown in FIG. 1, raw food waste 1 froma receiving pit is conveyed to shredder 2 where it is ground to the sizeof about ¼ inch (6 mm) or less to provide sufficient contact area forsubsequent processing. Ground waste is introduced by positivedisplacement, preferably, plunger pump 3 to equalization tank 4 equippedwith a submersible mixer, preferably, a propeller mixer. Theequalization tank can be either cylindrical (with flat or conicalbottom), rectangular or of any other shape providing uniform mixingthroughout the tank volume. A positive displacement, preferably, plungerpump 5, conveys the equalized raw food waste to mixer 6. Agglomeratingpolymer 13, preferably, a synthetic organic cationic polyamine orpolyDADMAC flocculant GRAS (generally recognized as safe) series dilutedto an effective concentration (e.g., from about 2.5 to 4.0 kg per dryton of waste, preferably, from about 2.9 to 3.2 kg/ton) in the solutionpreparation, and dosing unit 14 is introduced to mixer 6 in order toprovide initial floc agglomeration. Hydrated lime stored in silo 7 isdiluted to about 30% concentration in holding tank 8; then by dosingpump 9, it is introduced to mud tank 10. In tank 10 hydrated lime isdiluted to about a 5% concentration lime slurry, and the lime slurry isintroduced by pump 11, via feeding line 12, into mixer 6 for maintainingoptimum pH level, preferably, ranging from pH 8.0 to pH 9.0 maintainedby a pH control device 17. Bentonite is later introduced to mud tank 10simultaneously with lime, in order to provide faster and larger flocformation.

[0022] An anionic flocculant 15, preferably, a high molecular weight(e.g., from about 8-20 million, about 12-14 million preferred)polyacrylamide GRAS series, is diluted to an effective concentration(generally about 5 to 10 times less than the dosage of the cationicagglomerating polymer, preferably about 6 to 7 times less) in thesolution preparation and dosing unit 16 is introduced to mixer 6 inorder to provide floc formation, thus releasing free water (liquidphase) from the agglomerates. Mixer 6 operates as a batch reactor.Hydrated lime slurry is introduced simultaneously with the raw foodwaste; after 5-7 minutes of mixing, the agglomerating polymer isintroduced into the mixer, then the anionic flocculant is introduced tothe mixer following the agglomerating polymer, with an interval of about7-12 minutes. The agglomeration and flocculation reactions proceedwithin a residence time of 0.5 to 1.0 hours. The process induced inmixer 6 is a food waste conditioning process. The conditioned food wasteis conveyed by a positive displacement pump 18 to thickener 19, wherephase separation occurs. Liquid phase 28 screened from the conditionedfood waste and containing dissolved and colloidal matter, as well astiny suspended solids is conveyed to a separate treatment train, whilesolid phase 20, which is thickened food waste, is conveyed to solidphase mixer 21. A dry carrier 22, (e.g., millfeed (wheat midds),granulated cookie or other bakery products, corn, soy beans, maltsprouts, dried citrus pellets, or cocoa hulls) as a corrective agent isintroduced to mixer 21 for maintaining solid phase moisture, preferablyno higher than about 50%. Fat removed in the liquid phase treatmenttrain is discharged to mixer 21 for balancing the appropriatefat-to-protein ratio. Mixer 21 is considered a solid phase conditioningreactor. The conditioned solid phase is conveyed to pelletizer 23 wherewet solid phase pellets are formed by extruding. The wet solid phasepellets 24 are then conveyed to dryer 25, where water 26 is evaporated,and dry final product 27 as animal feed is distributed to the customers.

[0023] The liquid phase treatment train starts from liquid phaseequalization and holding tank 29 equipped with a submersible mixer,preferably a propeller mixer. The liquid phase equalization tankprevents undesirable premature phase separation, and it can be eithercylindrical (with flat or conical bottom), rectangular, or of any othershape providing uniform mixing throughout the tank volume. The equalizedliquid phase flow enters grease and fat recovery system 30 from whichremoved fat 48 is collected in a drum or container 49, while the fatfree liquid is directed to a chemical oxidation reactor 31. For chemicaloxidation of the dissolved and colloidal organic material contained inthe liquid phase, any strong oxidizer such as either hydrogen peroxide,ozone, or chlorine dioxide, or a combination of one of them withultraviolet radiation can be used. Pump 32 delivers liquid flowcontaining the oxidized organic material to physical-chemical treatment.A physical-chemical reactor including two or more compartments 33 and 34arranged in series is used for providing flocculation of the oxidizedparticles using a combination of cationic and anionic flocculants 43 and45 in solution, prepared in corresponding units 44 and 46 andintroduced, correspondingly, in said compartments. Compartments 33 and34 can be either complete mixing reactors or contact flocculationreactors as filters with the fixed or moving granular beds. In order toobtain high purity liquid phase treated effluent, carbon adsorptionreactor 35 and/or ion exchange reactor 36 follow the physical-chemicaltreatment reactor. Eventually, reactors 35 and 36 can be two-stage ionexchange reactors for subsequent removal of hardness and ammonia.Alternatively, the contact flocculation process can be implemented intwo stages with the upward stream filtration in the first stage (33 and34), and the downward stream filtration in the second stage (35 and 36).For the air-and-water backwash of the contact flocculation filters, aircompressor 47 is used, as well as final treated effluent 37 as processwater 38 for preparation of all reagent solutions. Process water 38 isstored in tank 53, and with pump 54 is used for filter backwash. Filterbackwash dirty water 50 is collected in tank 51, then by pump 52 isconveyed to mixer 6. If reactor 35 is an ion exchange reactor, asolution of acid or salt 39 is prepared in tank 41 equipped with afeeder 40 and dosing pump 42. Wastewater resulting from ion exchangematerial regeneration is, alternatively, collected in tank 51 anddischarged into mixer 6 for neutralization.

[0024] The following example illustrates the effectiveness of the systemand process of the present invention. The outcomes were based on theresults of a bench-scale test of the process of the present invention.The method was used for processing 100 tons per day of food waste intoanimal feed. This example is compared with that by U.S. Pat. No.5,596,815, herein incorporated by reference. The comparison isillustrated in Table 1. TABLE 1 Mass of material By Inventive System andProcess By U.S. Pat. No. 5,596,815 Points of the Process Tons of Tons ofTons of Flow Diagram solids Tons of water % moisture solids water %moisture Inlet (raw food waste) 26 74 74 26 74 74 Mixer (the second 2638 60 116 84 42 mixer by inventive method and the only mixer by theprototype) Pelletizer 32 38 54.3 116 84 42 Outlet Vapor — 33 — — 68 —Product 32 5 13.5 116 16 12.1

[0025] noted above, moisture of the raw food waste was decreased from74% to 60% by removing 36 tons of water with a screw press, using pHadjustment followed by addition of bentonite and by introduction of anappropriate flocculation means proven for animal food additives. Afurther decrease in moisture was provided by adding 6 tons of drycarriers. In contrast, the decrease in moisture of raw food waste from74% to 42% by U.S. Pat. No. 5,596,815 was provided by adding 100 tons ofdry carriers. The decrease in waste food moisture to approximately45-55% is necessary for following efficient pelletization. Thermaldrying of the pelletized product in order to obtain moisture of thefinal product of 12-13.5% is a costly and energy consuming process. Theamount of water to be evaporated by the inventive method was 33 tons,while that by U.S. Pat. No. 5,596,815 is 68 tons.

[0026] In further experiments, a pilot-scale test using industrial sizedewatering equipment—a screw press furnished with correspondingauxiliary equipment was employed. The method resulted in a substantialdecrease in the amount of dry carriers introduced as compared to theprocess of U.S. Pat. No. 5,596,815, as well as a substantial decrease inthe amount of evaporated water in the drying process. A batch of 460 lof shredded raw food waste was prepared and mixed with a mechanicalagitator in a 1,160 l mixer. For better mixing with the reagents, theraw food waste was diluted 30% by the process water. The addition of a30% hydrated lime slurry in the dosage of 10 g/l provided pH adjustmentto pH 8.0-9.0, which in turn provided enhanced flocculation. Bentonitein the dosage of 12 g/l (calculated relative to the amount of initialraw food waste) was introduced to the mixer. A 0.5% solution of the GRAS(generally recognized as safe) polymer 240G from Cytec Industries, Inc.was then introduced to the mixer. The dosage of the polymer was 1.9 kgper dry ton of the raw food waste. The processed admixture was dewateredin the screw press, resulting in the dewatered product moisture of 68%.Additional moisture reduction was provided by addition of a relativelysmall amount of an appropriate dry carrier.

[0027] In practice, there are four preferred unit operations andgeographic configurations for the manufacturing processes of the presentinvention: 1) Collection, shown as 100 in FIG. 2: The location wherefood waste collection trucks tip their loads. The site may be a transferstation (to consolidate raw waste for trucking to a central treatmentfacility) or a food waste processing plant; 2) Dewatering, shown as200-201 in FIG. 2: Preprocessing unit operations to include a manualpick line (to remove metal objects, metal foil, twist ties, waste paperand plastic, bones, etc.), grinding, dewatering, and optionalsterilization if the preprocessed waste is to be transported to a remotepelletizing plant; 3) Pelletizing and Drying, shown in 300-302 in FIG.2: Includes mixing, extruding (pelletizing), drying, conditioning,cooling, and applicable air emission controls. The pellets may beformulated as a functional feed (corn equivalent) or custom-blended andsold as a feed ingredient or complete feed; 4) Custom Blending, shown as400-403 in FIG. 2: Mixing of various feed ingredients to meet a customformulation for % protein, % fat, % fiber, and other nutrient targetsalong with feed additives (vitamins, antibiotics, growth hormones). Thepellets can be one of the feed ingredients.

[0028] Various geographic configurations are also shown in FIG. 2, whichillustrate alternative raw waste collection and transfer stations.

[0029] Configuration A—Transport Raw Food Waste: Raw food waste iscollected 100 and hauled in e.g., liquid tanker trucks to a singleprocessing facility, where subsequent dewatering 201, palletizing/drying301 and custom blending 401 take place, located near animal farms 500.

[0030] Configuration B—Transport Custom Feed: Raw food waste isprocessed (collected 100, dewatered 200 and pelletized/dried 300) andcustom blended 400 at the raw waste collection site.

[0031] Configuration C—Transport Dewatered Raw Waste: Raw food waste ispreprocessed (collected 100 and dewatered 200) at the raw wastecollection site. Dewatered waste is transported to a remote processingplant with pelletizing/drying 302 and custom blending 402 operations.

[0032] a particularly preferred embodiment of the present invention(Configuration D—Transport Food-from-Feed Pellets), raw food waste ispreprocessed (collected 100 and dewatered 200) and pelletized/dried 300at the same raw waste collection site. Dry, stable pellets aretransported to a remote processing plant with custom blending 403operations. This approach will likely yield the greatest processefficiencies.

[0033] While this invention has been described with respect toparticular embodiments thereof, it is apparent that numerous other formsand modifications of this invention will be obvious to those skilled inthe art. The appended claims and this invention generally should beconstrued to cover all such obvious forms and modifications which arewithin the true spirit and scope of the present invention.

I claim:
 1. A process for producing animal feed from food waste,comprising the steps of: (a) shredding of the food waste, resulting inground food waste; (b) thickening of the ground food waste through theuse of an amount, effective for the purpose, of an agglomerating polymerand a synthetic organic flocculant, resulting in a low moisture productand a separate liquid phase; (c) adding a dry carrier to the lowmoisture product; and (d) treating the liquid phase so as to provide ahigh purity effluent for recycling, wherein the ground food waste isshredded, thickened and dried at the same location.
 2. The process asrecited in claim 1, wherein the agglomerating polymer is selected fromthe group consisting of an organic cationic polyamine and a polyDADMACflocculent.
 3. The process as recited in claim 1, wherein the food wasteis ground to less than 6 millimeters.
 4. The process as recited in claim1, wherein said ground food waste provides sufficient contact area forsubsequent processing.
 5. The process as recited in claim 1, wherein thesynthetic organic flocculent is an anionic flocculent.
 6. The process asrecited in claim 1, wherein the pH of the system is about 8-9.
 7. Theprocess as recited in claim 1, wherein the anionic flocculent is a highmolecular weight polyacrylamide GRAS series.
 8. The process as recitedin claim 1, wherein a hydrated lime slurry is introduced with the groundfood waste.
 9. The process as recited in claim 1, wherein the drycarrier is selected from the group consisting of millfeed, bakeryproducts, corn, soy beans, malt sprouts, dried citrus pellets and cocoahulls.